Traveling hydraulic working machine

ABSTRACT

A modification torque computing unit  83  computes a modification torque ΔT and a torque converter speed ratio e is computed from input and output revolution speeds of a torque converter  31 . A first determination coefficient α corresponding to the speed ratio e, and a second determination coefficient β corresponding to a pump pressure are computed. A selector  87  selects the smaller one of these coefficients as a determination coefficient γ, and the modification torque ΔT is multiplied by γ to provide a modification torque ΔTA. An adder  89  adds the modification torque ΔTA (negative value) to a pump base torque TR to provide a modified pump base torque TRA, whereby a maximum pump absorption torque TRA is controlled so as to become TRA. The maximum pump torque reducing control can then be performed while accurately confirming a work situation during the combined operation of travel and a working actuator.

TECHNICAL FIELD

The present invention relates to a traveling hydraulic working machine,such as a wheel loader or a telescopic handler, in which a transmissionis driven by a prime mover (engine) to travel the machine and ahydraulic pump is also driven by the prime mover to operate a workingactuator, thereby carrying out predetermined work.

BACKGROUND ART

In a known general traveling hydraulic working machine, a hydraulic pumpis of the fixed displacement type, and the maximum absorption torque ofthe pump is also constant (fixed). Therefore, a proportion at which theengine output torque is distributed between respective operations of thehydraulic pump and travel (transmission) is constant and so is a maximumtorque for the travel.

In connection with such a known general traveling hydraulic workingmachine, Japanese Patent No. 2968558 proposes an improved one employinga variable displacement hydraulic pump in such a manner that the maximumabsorption torque of the hydraulic pump can be changed. According tothis related art, the sum of respective loads of a travel driving deviceand a working actuator (i.e., the sum of the absorption torque of thehydraulic pump and the transmission torque (travel torque)) is detected.When the load sum is smaller than the output torque of an engine, themaximum absorption torque of the variable displacement hydraulic pumpfor the working actuator is maintained at a setting value, and when theload sum becomes larger than the engine output torque, e.g., when themachine is in a combined stall state, the maximum absorption torque ofthe variable displacement hydraulic pump is reduced, while the traveltorque is increased to obtain a large tractive force. As a result, theengine output can be effectively utilized.

Patent Reference 1: Japanese Patent No. 2968558

DISCLOSURE OF THE INVENTION

One example of work carried out by a traveling hydraulic workingmachine, such as a wheel loader or a telescopic handler, is excavationof natural ground. In such excavation work, if a travel force can beincreased when a bucket is pushed into earth and sand, the bucket can bemore deeply pushed into the earth and sand, and the working efficiencycan be improve correspondingly. In the known general traveling hydraulicworking machine, because the maximum absorption torque of the hydraulicpump is constant (fixed), the travel force cannot be increased even inthe above-mentioned type work.

According to the related art disclosed in Japanese Patent No. 2968558,when the bucket is pushed into earth and sand during the excavation ofnatural ground, the machine comes into an operating state in which thesum of the absorption torque of the hydraulic pump and the travel torqueexceeds the engine output torque. Therefore, the maximum absorptiontorque of the hydraulic pump is reduced (hereinafter referred to as“maximum pump torque reducing control” for the sake of convenience), andthe travel torque is increased correspondingly. As a result, the travelforce can be increased and the working efficiency can be improved.However, the disclosed related art is designed just to detect the sum ofrespective loads of the travel driving device and the working actuator(i.e., the sum of the absorption torque of the hydraulic pump and thetravel torque). Accordingly, a satisfactory result is obtained inlimited types of work, whereas the workability deteriorates and theworking efficiency decreases in some type of work.

In work of scooping earth and sand under traveling, for example, theearth and sand are scooped into the bucket by utilizing the travel force(tractive force) to push the bucket into the earth and sand while anupper front force is applied to the bucket so as to raise the bucket.During such scooping work, when the sum of the absorption torque of thehydraulic pump and the travel torque exceeds the engine output torqueand the maximum pump torque reducing control is performed, the deliveryrate of the hydraulic pump is reduced and the bucket raising speed isslowed down, thus leading to a reduction in the amount of work carriedout.

Also, assuming the case that the front load is increased in a statewhere, for example, snow removing work is carried out at a constantspeed while lowering a boom, if the maximum pump torque reducing controlis performed, a larger travel force is produced and the snow removingwork cannot be carried out at the constant speed.

It is an object of the present invention to provide a travelinghydraulic working machine, which can perform the maximum pump torquereducing control while accurately confirming a work situation during thecombined operation of travel and a working actuator, and can maintainsatisfactory combination in work and improve both the workability andthe working efficiency.

(1) To achieve the above object, according to the present invention, ina traveling hydraulic working machine comprising at least one primemover, a machine body mounting the prime mover thereon, traveling meansprovided in the machine body and including a torque converter coupled tothe prime mover, a variable displacement hydraulic pump driven by theprime mover, at least one working actuator operated by a hydraulic fluidfrom the hydraulic pump, and an operating device for generating anoperation signal to control the working actuator, the travelinghydraulic working machine further comprises first detecting means fordetecting whether the sum of absorption torque of the hydraulic pump andtravel torque of the traveling means exceeds output torque of the primemover; second detecting means for detecting an operating situation ofthe traveling means; and pump torque modifying means for modifyingmaximum absorption torque of the hydraulic pump depending on theoperating situation of the traveling means detected by the seconddetecting means when the first detecting means detects that the sum ofthe absorption torque of the hydraulic pump and the travel torqueexceeds the output torque of the prime mover.

With those features, the first detecting means, the second detectingmeans and the pump torque modifying means are provided, and the maximumabsorption torque of the hydraulic pump is modified depending on theoperating situation of the traveling means detected by the seconddetecting means when the first detecting means detects that the sum ofthe absorption torque of the hydraulic pump and the travel torqueexceeds the output torque of the prime mover. Therefore, the maximumpump torque reducing control can be performed while accuratelyconfirming a work situation during the combined operation of travel anda working actuator. In addition, satisfactory combination in work can bemaintained and an improvement of both the workability and the workingefficiency can be realized.

(2) In above (1), preferably, the pump torque modifying means comprisesfirst means for computing a modification torque when the first detectingmeans detects that the sum of the absorption torque of the hydraulicpump and the travel torque exceeds the output torque of the prime mover,second means for modifying the modification torque depending on theoperating situation of the traveling means detected by the seconddetecting means, and third means for controlling the maximum absorptiontorque of the hydraulic pump to be reduced by an amount corresponding tothe modification torque modified by the second means.

With those features, when it is detected that the sum of the absorptiontorque of the hydraulic pump and the travel torque exceeds the outputtorque of the prime mover, the maximum pump torque reducing control isperformed depending on the operating situation of the traveling means.Therefore, the pump absorption torque can be reduced depending on theoperating situation of the traveling means so that the travel torque canbe increased.

(3) In above (2), preferably, the second detecting means is means fordetecting, as the operating situation of the traveling means, anoperating situation in which the traveling means requires what magnitudeof travel torque, and the second means modifies the modification torqueto be reduced or to become 0 when the second detecting means detectsthat the traveling means is in an operating situation not requiring arelatively large travel torque.

With those features, when the traveling means is in the operatingsituation not requiring a relatively large travel torque, the amount bywhich the maximum absorption torque of the hydraulic pump is reduced inthe maximum pump torque reducing control can be suppressed so as toincrease the amount of work carried out. When the traveling means is inan operating situation requiring a relatively large travel torque, themaximum absorption torque of the hydraulic pump is reduced in themaximum pump torque reducing control by an amount corresponding to themodification torque so that a larger travel torque can be obtained.

(4) Also in above (2), preferably, the second means modifies themodification torque to be variably reduced to 0 depending on themagnitude of travel torque required by the traveling means.

With that feature, since the amount by which the maximum absorptiontorque of the hydraulic pump is reduced is adjusted depending on themagnitude of travel torque required by the traveling means, the maximumpump torque reducing control can be performed in a finer manner.

(5) In above (1), preferably, the traveling hydraulic working machinefurther comprises third detecting means for detecting an operatingsituation of the working actuator, and the pump torque modifying meansmodifies the maximum absorption torque of the hydraulic pump dependingon the operating situation of the traveling means detected by the seconddetecting means and the operating situation of the working actuatordetected by the third detecting means when the first detecting meansdetects that the sum of the absorption torque of the hydraulic pump andthe travel torque exceeds the output torque of the prime mover.

Thus, since the third detecting means is further provided and the pumptorque modifying means modifies the maximum absorption torque of thehydraulic pump depending on the operating situation of the travelingmeans detected by the second detecting means and the operating situationof the working actuator detected by the third detecting means when thefirst detecting means detects that the sum of the absorption torque ofthe hydraulic pump and the travel torque exceeds the output torque ofthe prime mover, the maximum pump torque reducing control can beperformed while accurately confirming a work situation during thecombined operation of travel and a working actuator. In addition,satisfactory combination in work can be maintained and an improvement ofboth the workability and the working efficiency can be realized.

(6) In above (5), preferably, the pump torque modifying means comprisesfirst means for computing a modification torque when the first detectingmeans detects that the sum of the absorption torque of the hydraulicpump and the travel torque exceeds the output torque of the prime mover,second means for modifying the modification torque depending on theoperating situation of the traveling means detected by the seconddetecting means and the operating situation of the working actuatordetected by the third detecting means, and third means for controllingthe maximum absorption torque of the hydraulic pump to be reduced by anamount corresponding to the modification torque modified by the secondmeans.

With those features, when it is detected that the sum of the absorptiontorque of the hydraulic pump and the travel torque exceeds the outputtorque of the prime mover, the maximum pump torque reducing control isperformed depending on the operating situation of the traveling meansand the operating situation of the working actuator. Therefore, the pumpabsorption torque can be reduced depending on the operating situation ofthe traveling means and the operating situation of the working actuatorso that the travel torque can be increased.

(7) In above (6), preferably, the third detecting means is means fordetecting, as the operating situation of the working actuator, anoperating situation in which the working actuator requires whatmagnitude of pump delivery rate, and the second means modifies themodification torque to be reduced or to become 0 when the thirddetecting means detects that the working actuator is in an operatingsituation requiring a relatively large pump delivery rate.

With those features, when the working actuator is in the operatingsituation requiring a relatively large pump delivery rate, the amount bywhich the maximum absorption torque of the hydraulic pump is reduced inthe maximum pump torque reducing control can be suppressed so as toincrease the pump delivery rate, thereby increasing the amount of workcarried out. When the working actuator is in an operating situation notrequiring a relatively large pump delivery rate, the maximum absorptiontorque of the hydraulic pump is reduced in the maximum pump torquereducing control by an amount corresponding to the modification torqueso that a larger travel torque can be obtained.

(8) In above (6), preferably, the second means modifies the modificationtorque to be variably reduced to 0 depending on the magnitude of pumpabsorption torque required by the working actuator.

With that feature, since the amount by which the maximum absorptiontorque of the hydraulic pump is reduced is adjusted depending on themagnitude of pump absorption torque required by the working actuator,the maximum pump torque reducing control can be performed in a finermanner.

(9) In above (1), preferably, the first detecting means is means fordetecting whether a deviation between a target revolution speed and anactual revolution speed of the prime mover exceeds a preset value, andwhether the sum of the absorption torque of the hydraulic pump and thetravel torque of the traveling means exceeds the output torque of theprime mover is detected depending on whether the deviation between thetarget revolution speed and the actual revolution speed of the primemover exceeds the preset value.

(10) In above (1), preferably, the second detecting means includes meansfor detecting input and output revolution speeds of the torqueconverter, and means for computing a torque converter speed ratio fromthe input and output revolution speeds of the torque converter, and thesecond detecting means detects the operating situation of the travelingmeans based on the torque converter speed ratio.

(11) In above (5), preferably, the third detecting means includes meansfor detecting one of a delivery pressure of the hydraulic pump and adriving pressure of the working actuator, and the third detecting meansdetects the operating situation of the working actuator based on thedetected pressure.

(12) In above (5), preferably, the third detecting means includes meansfor detecting the operation signal generated by the operating device anddetects the operating situation of the working actuator based on thedetected operation signal.

ADVANTAGES OF THE INVENTION

According to the present invention, since the maximum absorption torqueof the hydraulic pump can be modified while confirming a work situationon the whole during the combined operation of travel and a workingactuator, it is possible to maintain satisfactory combination in workand improve both the workability and the working efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an overall system of a traveling hydraulicworking machine according to a first embodiment of the presentinvention.

FIG. 2 is a side view showing an external appearance of a telescopichandler, the view showing the case where a fork for use in loading andunloading work is mounted as an attachment.

FIG. 3 is a side view showing an external appearance of a telescopichandler, the view showing the case where a bucket for use in excavationwork and surface soil peeling-off work is mounted as an attachment.

FIG. 4 is a functional block diagram showing the processing function ofa controller in the first embodiment of the present invention.

FIG. 5 is a graph showing the setting relationship of the output torqueof a torque converter and the absorption torque of a hydraulic pump 12with respect to an engine output in the traveling hydraulic workingmachine according to the first embodiment.

FIG. 6 is a graph showing an operating state of the traveling hydraulicworking machine according to the first embodiment.

FIG. 7 is a graph showing an operating state of the traveling hydraulicworking machine according to the first embodiment.

FIG. 8 is a graph showing an operating state of the traveling hydraulicworking machine according to the first embodiment.

FIG. 9 is a graph showing an operating state of the traveling hydraulicworking machine according to the first embodiment.

FIG. 10 is a diagram showing an overall system of a traveling hydraulicworking machine according to a second embodiment of the presentinvention.

FIG. 11 is a functional block diagram showing the processing function ofa controller in the second embodiment of the present invention.

REFERENCE NUMERALS

1 prime mover (engine)

2 working system

3 traveling system

4, 4A control system

12 hydraulic pump

13, 14, 15, 16 hydraulic actuator

17, 18, 19, 20 direction control valve

23, 24, 25, 26 control lever unit

28 torque control regulator

29 torque control solenoid valve

31 torque converter

32 transmission

33, 34 differential gear

35 front wheel

36 rear wheel

42 accelerator pedal

43 position sensor

44 pressure sensor

45, 46 revolution sensor

48, 48A controller

61 pressure sensor

80 target revolution speed computing unit

81 base torque computing unit

82 revolution speed deviation computing unit

83 modification torque computing unit

84 speed ratio computing unit

85 traveling state determining unit

86 working state determining unit

87 selector

88 multiplier

89 adder

91 second working state determining unit

92 multiplier

101 machine body

102 cab

103 boom

104 fork (attachment)

105 bucket (attachment)

200 earth and sand

201 surface earth and sand

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings.

FIG. 1 is a diagram showing an overall system of a traveling hydraulicworking machine according to a first embodiment of the presentinvention.

FIG. 1, the traveling hydraulic working machine according to thisembodiment comprises a diesel engine (hereinafter referred to simply asan “engine”) 1 serving as a prime mover, a working system 2 and atraveling system 3 both driven by the engine 1, and a control system 4.

The engine 1 includes an electronic governor 41, and the electronicgovernor 41 adjusts a fuel injection amount depending on a control inputapplied from an accelerator pedal 42 (i.e., an accelerator controlinput), to thereby regulate the revolution speed of the engine 1. Inother words, the accelerator pedal 42 serves as a means operated by anoperator and commanding an engine revolution speed as a target(hereinafter referred to simply as a “target revolution speed”). Thetarget revolution speed is set depending on the amount by which theaccelerator pedal is pressed down (i.e., an accelerator pressed-downamount).

The working system 2 comprises a hydraulic pump 12 driven by the engine1, a plurality of hydraulic actuators (working actuators) 13, 14, 15 and16 operated by a hydraulic fluid delivered from the hydraulic pump 12,directional control valves 17, 18, 19 and 20 disposed respectivelybetween the hydraulic pump 12 and the plurality of hydraulic actuators13, 14, 15 and 16 to control flows of the hydraulic fluid supplied tothe corresponding actuators, a plurality of control lever units 23, 24,25 and 26 for respectively shifting the directional control valves 17,18, 19 and 20 and generating pilot pressures (operation signals) tocontrol the hydraulic actuators 13, 14, 15 and 16, and a pilot hydraulicpump 27 for supplying a hydraulic fluid, which serves to provide anoriginal pressure, to the control lever units 23, 24, 25 and 26.

The hydraulic pump 12 is of the variable displacement type and includesa torque control regulator 28. The torque control regulator 28 controlsthe tilting (displacement) of the hydraulic pump 12 such that, when thedelivery pressure of the hydraulic pump 12 rises, the tilting(displacement) of the hydraulic pump 12 is reduced correspondingly toavoid the absorption torque of the hydraulic pump 12 from exceeding asetting value (maximum pump absorption torque). The setting value(maximum pump absorption torque) of the torque control regulator 28 isvariable and controlled by a torque control solenoid valve 29. Thetorque control solenoid valve 29 is operated by an electric commandsignal and outputs a control pressure corresponding to the electriccommand signal with the delivery pressure of the pilot hydraulic pump 27serving as a hydraulic pressure source.

The traveling system 3 comprises a torque converter 31 coupled to anoutput shaft of the engine 1 in series with respect to the hydraulicpump 12, a transmission (T/M) 32 coupled to an output shaft of thetorque converter 31, and front wheels 35 and rear wheels 36 which arecoupled to the transmission 32 respectively through differential gears33, 34.

The control system 4 comprises a position sensor 43 for detecting theamount by which the accelerator pedal 42 is pressed down (i.e., theaccelerator pressed-down amount), a pressure sensor 44 for detecting, asan operating situation of the hydraulic actuator, the delivery pressureof the hydraulic pump 12, a revolution sensor 45 for detecting an outputrevolution speed of the engine 1 (i.e., an input revolution speed of thetorque converter 31), a revolution sensor 46 for detecting an outputrevolution speed of the torque converter 31, and a controller 48. Thecontroller 48 has the engine control function of outputting, inaccordance with a signal from the position sensor 43, a command signalto the electronic governor of the engine 1 so that the revolution speedcorresponding to the accelerator pressed-down amount is obtained, andthe pump control function of executing predetermined arithmetic andlogical operations based on signals from the position sensor 43, thepressure sensor 44 and the revolution sensors 45, 46, and outputting acommand signal to the torque control solenoid valve 29.

FIGS. 2 and 3 each show an external appearance of a telescopic handler(also called a lift truck).

In this embodiment, the traveling hydraulic working machine is, by wayof example, a telescopic handler. The telescopic handler comprises amachine body 101, a cab 102 located on the machine body 101, anextendable boom 103 mounted to the machine body 101 in a manner capableof pivotally rising and lowering laterally of the cab 102, and anattachment 104 or 105 rotatably mounted to a fore end of the boom 103.The front wheels 35 and the rear wheels 36 are mounted to the machinebody 101, and the telescopic handler travels with the front wheels 35and the rear wheels 36 driven by the motive power of the engine 1. Theboom 103 and the attachment 104 or 105 constitute a working device. Theattachment 104 shown in FIG. 2 is a fork for use in loading andunloading work, and the attachment 105 shown in FIG. 3 is a bucket foruse in, e.g., excavation work and surface soil peeling-off work.

Returning to FIG. 1, the hydraulic actuators 13, 14 and 15 are, by wayof example, a boom cylinder, a telescopic cylinder, and an attachmentcylinder, respectively. The boom 103 is pivotally raised or lowered withextension or contraction of the boom cylinder 13, and is extended orcontracted with extension or contraction of the telescopic cylinder 14.The attachment 104 or 105 is tilted with extension or contraction of theattachment cylinder 15. The hydraulic actuator 16 shown in FIG. 1 is ahydraulic motor for rotating a sweeper brush, for example, when asweeper is used as the attachment. Those components, such as the engine1, the hydraulic pump 12, the torque converter 31, and the transmission32, are mounted to the machine body 101.

In the following description, the attachment 104 or 105 is referred toas the “front” for the sake of convenience, and a force applied from thehydraulic actuators 13, 14 and 15 to move the attachment 104 or 105 isreferred to as a “front force” for the sake of convenience. Also, workcarried out with the movement of the attachment 104 or 105 is referredto as “front work”.

FIG. 4 is a functional block diagram showing the processing function ofthe controller 48 related to pump control.

In FIG. 4, the controller 48 has various functions of a targetrevolution speed computing unit 80, a base torque computing unit 81, arevolution speed deviation computing unit 82, a modification torquecomputing unit 83, a speed ratio computing unit 84, a traveling statedetermining unit 85, a working state determining unit 86, a selector 87,a multiplier 88, and an adder 89.

The target revolution speed computing unit 80 receives a detected signalof the accelerator pressed-down amount from the position sensor 43 andrefers to a table, which is stored in a memory, based on the receivedinput, thereby computing a target engine revolution speed NRcorresponding to the accelerator pressed-down amount at that time. Thetarget revolution speed NR represents the engine revolution speedintended by the operator during work. In the table stored in the memory,the relationship between the target revolution speed NR and theaccelerator pressed-down amount is set such that the target revolutionspeed NR is increased as the accelerator pressed-down amount increases.

The base torque computing unit 81 receives the target engine revolutionspeed NR and refers to a table, which is stored in a memory, based onthe received input, thereby computing a pump base torque TRcorresponding to the target revolution speed NR at that time. In thetable stored in the memory, the relationship between NR and TR is setsuch that the pump base torque TR is increased as the target enginerevolution speed NR rises.

The revolution speed deviation computing unit 82 subtracts the targetengine revolution speed NR computed by the target revolution speedcomputing unit 80 from an actual engine revolution speed NA detected bythe revolution sensor 45, thereby computing an engine revolution speeddeviation ΔN (=NA−NR).

The modification torque computing unit 83 receives the revolution speeddeviation ΔN computed by the revolution speed deviation computing unit82, and refers to a table, which is stored in a memory, based on thereceived input, thereby computing a modification torque ΔT correspondingto the revolution speed deviation ΔN at that time. The modificationtorque ΔT is set with such an intention that, when the machine comesinto a high-load operating state in which the hydraulic pump 12 consumesthe maximum absorption torque and the sum of the pump absorption torque(i.e., the work load) and the input torque of the torque converter 31(i.e., the travel torque) exceeds the engine output torque, the maximumabsorption torque of the hydraulic pump 12 is reduced and the traveltorque is increased so as to provide a larger tractive forcecorrespondingly. In the table stored in the memory, the relationshipbetween ΔN and ΔT is set as follows. When the actual engine revolutionspeed NA is matched with the target engine revolution speed NR and therevolution speed deviation ΔN is 0, ΔT=0 is set. When the amount bywhich the actual engine revolution speed lowers is increased and therevolution speed deviation ΔN exceeds below a first setting value in aregion where the revolution speed deviation ΔN has a negative value, themodification torque ΔT is gradually reduced from 0 in a region ofnegative value as the revolution speed deviation ΔN decreases. When therevolution speed deviation ΔN exceeds below a second setting value (<the first setting value), the modification torque ΔT is held at aconstant value, i.e., ΔT=ΔTC.

The speed ratio computing unit 84 receives detected signals of the inputand output revolution speeds of the torque converter 31 from therevolution speed sensors 45, 46, respectively, and computes e=outputrevolution speed/input revolution speed, thereby obtaining a toqueconverter speed ratio e.

The traveling state determining unit 85 receives the toque converterspeed ratio e computed by the speed ratio computing unit 83, and refersto a table, which is stored in a memory, based on the received input,thereby computing a first determination coefficient a corresponding tothe toque converter speed ratio e at that time. The first determinationcoefficient α is set with intent to limit the modification of the pumpabsorption torque (i.e., the reduction of the pump maximum absorptiontorque), which is made in accordance with the modification torque ΔTwhen the toque converter speed ratio e is not small (when the torqueconverter 31 is not in a nearly stall state), i.e., in an operatingsituation where the travel system 3 does not require a large travelforce (travel torque). In the table stored in the memory, therelationship between e and α is set as follows. When the toque converterspeed ratio e is smaller than a first setting value, α=1 is set. Whenthe toque converter speed ratio e exceeds a second setting value (> thefirst setting value), α=0 is set. When the toque converter speed ratio eis between the first setting value and the second setting value, α isreduced at a predetermined proportion (gain) as the toque converterspeed ratio e increases.

The working state determining unit 86 receives a detected signal of thepump pressure from the pressure sensor 44, and refers to a table, whichis stored in a memory, based on the received input, thereby computing asecond determination coefficient β corresponding to the pump pressure atthat time. The second determination coefficient β is set with intent tolimit the modification of the pump absorption torque (i.e., thereduction of the pump maximum absorption torque), which is made inaccordance with the modification torque ΔT when the delivery pressure ofthe hydraulic pump 12 is not so high (when the work load is not solarge), i.e., in an operating situation where the working system 2requires a relatively large pump delivery rate. In the table stored inthe memory, the relationship between the pump pressure and β is set asfollows. When the pump pressure is lower than a first setting value, β=0is set. When the pump pressure exceeds a second setting value (> thefirst setting value), β=1 is set. When the pump pressure is between thefirst setting value and the second setting value, β is reduced at apredetermined proportion (gain) as the pump pressure lowers.

The selector 87 selects smaller one of the first determinationcoefficient α and the second determination coefficient β, and sets theselected one as a determination coefficient γ. Additionally, when thefirst determination coefficient α and the second determinationcoefficient β are equal to each other, the selector 87 selects one ofthem, e.g., α, in accordance with the preset logic.

The multiplier 88 multiplies the modification torque ΔT computed by themodification torque computing unit 83 by the determination coefficient γgiven as an output of the selector 87, thus providing a modificationtorque ΔTA.

The adder 89 adds the modification torque ΔTA (negative value) to thepump base torque TR computed by the base torque computing unit 80, thuscalculating a modified pump base torque TRA. The modified pump basetorque TRA is converted to a command signal for the torque controlsolenoid valve 29 in accordance with a known method, and the commandsignal is outputted to the torque control solenoid valve 29. The torquecontrol solenoid valve 29 outputs, to the torque control regulator 28, acontrol pressure corresponding to the command signal to make anadjustment such that the maximum pump absorption torque set in thetorque control regulator 28 becomes TRA.

In the construction described above, the revolution speed sensor 45, thetarget revolution speed computing unit 80, the revolution speeddeviation computing unit 82, and the modification torque computing unit83 constitute first detecting means for detecting whether the sum of theabsorption torque of the hydraulic pump 12 and the travel torque of thetraveling system 3 (traveling means) exceeds the output torque of theengine (prime mover) 1. The revolution speed sensors 45, 46, the speedratio computing unit 84, and the traveling state determining unit 85constitute second detecting means for detecting the operating situationof the traveling system 3. The modification torque computing unit 83,the multiplier 88, and the adder 89 constitute pump torque modifyingmeans for modifying the maximum absorption torque of the hydraulic pump12 depending on the operating situation of the traveling system 3detected by the second detecting means when the first detecting meansdetects that the sum of the absorption torque of the hydraulic pump 12and the travel torque exceeds the output torque of the prime mover 1.

The modification torque computing unit 83 constitutes first means forcomputing a modification torque when the first detecting means detectsthat the sum of the absorption torque of the hydraulic pump 12 and thetravel torque exceeds the output torque of the prime mover 1, themultiplier 88 constitutes second means for modifying the modificationtorque depending on the operating situation of the traveling means 3detected by the second detecting means, and the adder 89 constitutesthird means for controlling the maximum absorption torque of thehydraulic pump 12 to be reduced by an amount corresponding to themodification torque modified by the second means (88).

The pressure sensor 44 and the working state determining unit 86constitute third detecting means for detecting operating situations ofthe working actuators 13 to 16. The pump torque modifying means (i.e.,the modification torque computing unit 83, the multiplier 88, and theadder 89) modifies the maximum absorption torque of the hydraulic pump12 depending on the operating situation of the traveling system 3detected by the second detecting means and the operating situations ofthe working actuators 13 to 16 detected by the third detecting meanswhen the first detecting means detects that the sum of the absorptiontorque of the hydraulic pump 12 and the travel torque exceeds the outputtorque of the prime mover 1. In that case, the selector 87 and themultiplier 88 constitute second means for modifying the modificationtorque depending on the operating situation of the traveling meansdetected by the second detecting means and the operating situations ofthe working actuators 13 to 16 detected by the third detecting means.

With reference to FIG. 5, a description is made of the settingrelationship between the output torque of the torque converter 31(hereinafter referred to as the “torque converter torque” for the sakeof convenience) and the absorption torque of the hydraulic pump 12(hereinafter referred to as the “torque converter torque” for the sakeof convenience) in the traveling hydraulic working machine according tothis embodiment. In FIG. 5, the horizontal axis represents therevolution speed of the engine 1, and the vertical axis represents thetorque. Also, TE represents the output torque of the engine 1(hereinafter referred to as the “engine torque” for the sake ofconvenience) in a full load region where the fuel injection amount ofthe electronic governor 41 is maximized, and TR represents the outputtorque of the engine 1 (hereinafter referred to as the “engine torque”for the sake of convenience) in a regulation region corresponding to astage before the fuel injection amount of the electronic governor 41 ismaximized. Further, TT represents the output torque of the torqueconverter 31 (i.e., the torque converter torque), and TP represents themaximum absorption torque of the hydraulic pump 12 (hereinafter referredto as the maximum pump torque” for the sake of convenience).

The torque converter torque TT shown in FIG. 5 represents one resultingwhen the torque converter 31 is in a stall state (where the outputrevolution speed is 0 and the speed ratio e=0 holds). As the hydraulicworking machine starts traveling and the speed ratio increases from 0,the characteristic curve is shifted in the direction of an arrow X,shown in FIG. 5, such that the torque converter torque TT is reduced.The maximum pump torque TP shown in FIG. 5 represents torque (TPmax)resulting when the accelerator pedal 42 is pressed down in a maximumstroke to set the target revolution speed of the engine 1 to a maximumrated revolution speed NO and the modification torque ΔTA computed bythe multiplier 88 is 0. As the amount by which the accelerator pedal 42is pressed down is lessened to reduce the engine revolution speed, thetarget revolution speed NR computed by the target revolution speedcomputing unit 80 is also reduced and so is the base torque TR computedby the base torque computing unit 81. Accordingly, the maximum pumptorque PT decreases as indicated by an arrow Y in FIG. 5. Further, asthe modification torque ΔT decreases from 0 (namely, as an absolutevalue of ΔTA increases), the modified pump base torque TRA is reduced,and therefore the maximum pump torque TP decreases likewise as indicatedby the arrow Y in FIG. 5.

In the case of the traveling hydraulic working machine equipped with thetorque converter as in this embodiment, the travel force (tractiveforce) is very important. Hence, the engine 1 is selected to be of thetype that the output torque (point B) at the maximum rated revolutionspeed N0 is larger than a maximum value (point A) of the torqueconverter torque with a large allowance. On the other hand, the maximumpump torque is decided depending on excavation balance (i.e., balancebetween the travel/tractive force and the front force) during work usingthe bucket, and it is basically provided as a value (point C) smallerthan the torque converter torque. The engine revolution speed at thepoint A is N1 (>N0), and the engine revolution speed at the point C isN2 (>N0). In the traveling hydraulic working machine equipped with thetorque converter, therefore, the revolution speed of the engine 1 iskept from becoming below the target rated revolution speed N0 not onlyin the front sole operation, but also in the travel sole operation.

The operation of this embodiment will be described below.

FIGS. 6 to 9 show the operating state of the traveling hydraulic workingmachine according to this embodiment. FIGS. 6 to 8 each represent thecase where the accelerator pedal 42 is pressed down substantially in amaximum stroke to set the target engine revolution speed NR to the ratedrevolution speed N0, while FIG. 9 represents the case where theaccelerator pedal 42 is pressed down substantially half to set anintermediate target revolution speed NM. Also, FIGS. 6 and 9 eachrepresent the case where the torque converter 31 is in the stall stateand the speed ratio e is given as e=0, while FIGS. 7 and 8 eachrepresent the case where the torque converter 31 has a certain outputrevolution speed and the speed ratio e is given as e=about 0.3 ande=about 0.7, respectively.

In FIGS. 6 to 9, TEP represents the remainder obtained by subtractingTPmax from TE, i.e., the engine torque that is available by the torqueconverter 31 (on the travel side) when the hydraulic pump 12 consumesthe maximum absorption torque TP. TPmin represents the maximum pumptorque resulting when the maximum pump torque TP is reduced by an amountcorresponding to the modification torque ΔTC, and TEPA represents theremainder obtained by subtracting TPmin from TE, i.e., the engine torquethat is available by the torque converter 31 when the maximum pumptorque TP is reduced by an amount corresponding to the modificationtorque ΔTC. When the modification torque ΔTA varies between 0 and ΔTC,the maximum absorption torque TP of the hydraulic pump 12 is changedbetween TPmax and TPmin, and the engine torque available by the torqueconverter 31 is changed between TEP and TEPA.

<Operating State 1: Point A or Point D in FIG. 6>

When the front work is not performed even with the torque converter 31being in the stall state (e=0), or when the pump delivery pressure islow and the pump torque consumed by the hydraulic pump 12 is small evenduring the front work, the relationship of (engine torque≧torqueconverter torque+pump torque) holds. In this case, the engine revolutionspeed is not reduced, and the matching point between the travel load andthe pump load (actuator load) is positioned near a point A or a point Din FIG. 6, i.e., near an intersection between the curve representing TTand a straight line extended upward from the rated revolution speed N0.On that occasion, the revolution speed deviation computed by therevolution speed deviation computing unit 82 in FIG. 4 is provided asΔN≈0, and the modification torque computed by the modification torquecomputing unit 83 is provided as ΔT=0. Accordingly, the maximum pumptorque TP is not reduced.

<Operating State 2: Point F in FIG. 6>

When the torque converter 31 is in the stall state (e=0) and the torqueconsumed by the hydraulic pump 12 is increased to such an extent thatthe relationship of (engine torque<torque converter torque+pump torque)holds, the engine 1 comes into an overload state and the actual enginerevolution speed NA is slowed down. Therefore, the revolution speeddeviation computing unit 82 in FIG. 4 computes the revolution speeddeviation ΔN<0, and the modification torque computing unit 83 computesthe modification torque ΔT>0, e.g., ΔT=ΔTC. Also, because the speedratio e=0 is held and the pump pressure during the front work is high,the traveling state determining unit 85 computes the first determinationcoefficient α=1, the working state determining unit 86 computes thesecond determination coefficient β=1, and the selector 87 selects thedetermination coefficient γ=1. As a result, the multiplier 88 computesthe modification torque ΔTA=ΔT, e.g., ΔTA=ΔTC. Responsively, the maximumpump torque TP is reduced by an amount corresponding to ΔTC and becomesTPmin. This increases, to TEPA, the engine torque that is available bythe torque converter 31 when the hydraulic pump 12 consumes the maximumpump torque TP. In this case, therefore, the matching point between thetravel load and the pump load is positioned at a point F., i.e., anintersection between the curve representing TT (e=0) and a curverepresenting TEPA, and the engine revolution speed is reduced from therated revolution speed N0 to N4.

Looking at the known general traveling hydraulic working machineemploying the fixed displacement hydraulic pump, in the same operatingstate as that described above, the maximum pump torque TP is not changedand the engine torque available by the torque converter 31 remains atTEP. Therefore, the matching point between the travel load and the pumpload is positioned at a point E, i.e., an intersection between the curverepresenting TT (e=0) and a curve representing TEP, and the enginerevolution speed is reduced to N3 (<N4).

When the torque converter 31 is in the stall state where e=0 holds, workrequiring the travel/tractive force (i.e., the pushing force), such asexcavation of natural ground, is carried out in many cases. In the knowngeneral traveling hydraulic working machine, the maximum pump torque TPis not changed and the engine torque available by the torque converter31 remains at TEP. Therefore, the travel/tractive force (i.e., thepushing force) cannot be increased. In contrast, according to thisembodiment, since the travel force (tractive force) is increased fromTEP to TEPA, a larger tractive force can be ensured in the operatingstate requiring the tractive force, such as occurred in excavation ofnatural ground, and the engine output can be effectively utilized.

<Operating State 3: Point G in FIG. 7>

Also, in the case where the speed ratio of the torque converter 31 ise=about 0.3 and the relationship of (engine torque<torque convertertorque+pump torque) holds, the engine 1 comes into an overload state andthe actual engine revolution speed NA is slowed down. Therefore, therevolution speed deviation computing unit 82 in FIG. 4 computes therevolution speed deviation ΔN<0, and the modification torque computingunit 83 computes the modification torque ΔT>0, e.g., ΔT=ΔTC. On theother hand, assuming here that the traveling state determining unit 85has the second setting value<0.3, the traveling state determining unit85 computes the first determination coefficient α=0, and the selector 87selects the determination coefficient γ=0. As a result, the multiplier88 computes the modification torque ΔTA=0. Responsively, the maximumpump torque TP is not reduced and remains at TPmax. This keeps, at TEP,the engine torque that is available by the torque converter 31 when thehydraulic pump 12 consumes the maximum absorption torque TP. In thiscase, therefore, the matching point between the travel load and the pumpload is positioned at a point G, i.e., an intersection between a curverepresenting TT (e=0.3) and a curve representing TEP in FIG. 7.

Looking at the related art disclosed in Japanese Patent No. 2968558, inthe same operating state as that described above, because the actualtraveling state is not taken into consideration, the maximum absorptiontorque TP is reduced and the engine torque available by the torqueconverter 31 is increased to TEPA, similarly to the case of OperatingState 2, as soon as the relationship of (engine torque<torque convertertorque+pump torque) holds. Therefore, the matching point between thetravel load and the pump load is positioned at a point H, i.e., anintersection between the curve representing TT (e=0.3) and a curverepresenting TEPA.

When the machine is in the traveling state of e=about 0.3, it isadvantageous in many cases that the engine torque is supplied to thehydraulic pump at a larger proportion for the purpose of increasing theamount of work carried out. With the related art disclosed in JapanesePatent No. 2968558, even in such a case, the maximum pump torque TP isreduced and the engine torque available by the torque converter 31 isincreased to TEPA, thus resulting in a reduction in the amount of workcarried out on the pump side. In contrast, according to this embodiment,the maximum pump torque TP is not reduced and the hydraulic pump 12 canincrease the pump torque up to the maximum TP. It is hence possible toensure a large front force and to increase the amount of work carriedout.

<Operating State 4: Point I in FIG. 8>

Even in the case of the accelerator pedal 42 being pressed down in amaximum stroke to set the rated revolution speed N0 such that themaximum torque converter torque can be produced, in the traveling stateof e=about 0.7, the relationship of (engine torque>torque convertertorque+pump torque) is held and the engine revolution speed is notreduced. Therefore, the matching point between the travel load and thepump load is positioned at a point I, i.e., an intersection between acurve representing TT (e=0.7) and a straight line extended upward fromthe rated revolution speed N0 in FIG. 8. In such an operating state,there is an allowance in the engine torque even when the hydraulic pump12 consumes the maximum pump torque TP. It is hence not required toreduce the maximum pump torque TP.

With this embodiment, in the case described above, the revolution speeddeviation computed by the revolution speed deviation computing unit 82is provided as ΔN≈0, and therefore the modification torque computed bythe modification torque computing unit 83 is provided as ΔT=0 similarlyto the case of Operating State 1. Accordingly, the maximum pump torqueTP is not reduced.

<Operating State 5: Point J in FIG. 9>

When the accelerator pedal 42 is pressed down substantially half to setthe intermediate target revolution speed NM, the output torque isprovided as a value proportional to the revolutions based oncharacteristics of the torque converter 31 even with the torqueconverter 31 being in the stall state and the speed ratio e being givenas e=0. Therefore, the torque converter torque capable of beingdeveloped is reduced and the relationship of (engine torque>torqueconverter torque+pump torque) is held. As a result, the enginerevolution speed is not reduced and the matching point between thetravel load and the pump load is positioned at a point J, i.e., anintersection between the curve representing TT (e=0) and a straight lineextended upward from a target engine revolution speed N0M in FIG. 9.Also in this case, there is an allowance in the engine torque even whenthe hydraulic pump 12 consumes the maximum pump torque TP. It is hencenot required to reduce the maximum pump torque TP.

In such an operating state, depending on conditions, the traveling statedetermining unit 85 computes the first determination coefficient α=1,the working state determining unit 86 computes the second determinationcoefficient β=1, and the selector 87 selects the determinationcoefficient γ=1. With this embodiment, on that occasion, the revolutionspeed deviation computed by the revolution speed deviation computingunit 82 is provided as ΔN≈0, and therefore the modification torquecomputed by the modification torque computing unit 83 is provided asΔT=0. Accordingly, the modification torque ΔTA computed by themultiplier 88 is 0 and the maximum pump torque TP is not reduced. Thus,since the hydraulic pump 12 can increase the pump torque up to themaximum TPmax, it is possible to ensure a large front force and toincrease the amount of work carried out.

Practical work examples according to this embodiment will be describedbelow.

WORK EXAMPLE 1

One example of work carried out with the bucket 105 (see FIG. 3) mountedas the front attachment is excavation of natural ground. In theexcavation work, the bucket 105 serving as the front attachment ispushed into earth and sand (excavation target) by the travel force(tractive force) while the accelerator pedal 42 is operated to controlthe engine revolution speed, and an upward front force is then appliedto the bucket 105, causing the bucket to gradually run off upward,whereby the earth and sand is excavated. During a bucket pushingoperation in the excavation work, the torque converter 31 comes into acombined stall state and the relationship of (engine torque<torqueconverter torque+pump torque) holds. The term “combined stall state”means a state where the torque converter 31 is in the stall state (e=0)and the hydraulic pump 12 is in a relief state in which the deliverypressure of the hydraulic pump 12 rises up to the setting pressure of amain relief valve (not shown).

In the known general traveling hydraulic working machine, the maximumabsorption torque of the hydraulic pump is constant (fixed). In thecombined stall state, therefore, the matching point is positioned at thepoint E in FIG. 6 and the engine revolution speed is given as N3. Then,the output torque of the engine 1 is employed by the hydraulic pump 12with priority.

According to this embodiment, when the torque converter 31 comes intothe combined stall state during the bucket pushing operation in theexcavation work, the engine revolution speed is reduced and themodification torque computing unit 83 computes the modification torqueΔT=ΔTC. Also, at this time, because of being in the combined stallstate, the speed ratio computing unit 84 computes e≈0 as the speed ratioe, the traveling state determining unit 85 computes α=1 as the firstdetermination coefficient α. Further, because of the hydraulic pump 12being in the relief state, the working state determining unit 86computes β=1 as the second determination coefficient β, and the selector87 outputs γ=1 as the determination coefficient γ. Therefore, themultiplier 88 computes the modification torque ΔTA=ΔT, and the adder 89computes, as the modified base torque TRA, an added value of the basetorque TR computed by the base torque computing unit 81 and themodification torque ΔTA (=ΔTC) (i.e., a value obtained by subtracting anabsolute value of ΔTA from TR). In other words, the modified base torqueTRA is reduced by an amount corresponding to the modification torqueΔTC. As a result, the maximum pump torque TP is reduced to TPmin and theengine torque TEP available for the travel is increased to TEPAindicated by a broken line from a solid line shown in FIG. 6, wherebythe matching point is positioned at the point F in FIG. 6. Thus, thetorque converter torque is increased to increase the tractive force, andthe engine output can be effectively utilized.

Further, in an operation of raising the bucket after the bucket pushingoperation, the delivery pressure of the hydraulic pump 12 lowers. Onthis occasion, because of the working state determining unit 86 settingtherein the relationship between the pump pressure and the determinationcoefficient β such that β is reduced at a predetermined gain as the pumppressure lowers, when the delivery pressure of the hydraulic pump 2becomes lower than the second setting value set in the working statedetermining unit 86, a value of 0<β<1 depending on the pump pressure iscomputed as the determination coefficient β. In this case, therefore,the relationship of α>β is held, whereby the selector 87 selects thedetermination coefficient β and outputs γ=β as the determinationcoefficient γ. Responsively, the multiplier 88 computes the modificationtorque ΔTC (negative value) as a value increased depending on β (i.e.,ΔTC having a decreased absolute value), and the maximum pump torque TPis increased from TPmin. As a result, in comparison with the case ofβ=1, the delivery rate of the hydraulic pump 12 is increased to raisethe bucket speed, thus leading to the increased amount of work carriedout. Although the travel force is reduced in this case, such a reductionof the travel force is of no problem because the machine is now in theoperation of raising the bucket after the bucket pushing operation.Stated another way, since the amount by which the maximum pump torque TPis reduced is adjusted depending on a magnitude of the pump deliveryrate demanded by the working system 2, it is possible to perform themaximum pump torque reducing control in a finer manner and to furtherimprove the workability. In addition, the pump delivery rate or thetravel torque can be prevented from changing abruptly.

WORK EXAMPLE 2

Another example of work carried out using the bucket 105 is work ofscooping earth and sand while traveling. In the scooping work, thebucket 105 is pushed into earth and sand (excavation target) by thetravel force (tractive force) while the accelerator pedal 42 is operatedto control the engine revolution speed, and at the same time an upwardfront force is applied to the bucket 105 so as to raise it, whereby theearth and sand is scooped into the bucket. In such work of scoopingearth and sand while traveling, the machine is in the traveling statewhere the speed ratio of the torque converter 31 is, e.g., about 0.3.However, because the bucket is pushed into the earth and sand at thesame time, the torque converter torque is required to be a relativelylarge torque. Further, because the bucket 105 is raised upward whilebeing pushed into the earth and sand, the delivery pressure of thehydraulic pump 12 (i.e., the work load) rises up to nearly the reliefpressure. This holds the relationship of (engine torque<torque convertertorque+pump torque).

In the related art disclosed in Japanese Patent No. 2968558, when therelationship of (engine torque<torque converter torque+pump torque) isheld, this state is detected depending on a reduction of the enginerevolution speed. Responsively, the maximum pump torque TP isimmediately reduced to TPmin and the engine torque available by thetorque converter 31 is increased to TEPA. Therefore, the pump torque isreduced and the matching point is positioned at the point H in FIG. 7,whereby the delivery rate of the hydraulic pump 12 is reduced. Thisresults in the problem that the bucket raising speed is slowed down andthe amount of work carried out is reduced.

According to this embodiment, in the work scooping earth and sand whiletraveling, even when the engine revolution speed is reduced upon therelationship of (engine torque<torque converter torque+pump torque)being held and the modification torque computing unit 83 computes themodification torque ΔT=ΔTC, the speed ratio computed by the speed ratiocomputing unit 84 is given as e=about 0.3 and the speed ratio e islarger than (>) the second setting value of the traveling statedetermining unit 85. Therefore, the traveling state determining unit 85computes α=0 as the first determination coefficient α, and the selector87 outputs γ=0 as the determination coefficient γ. The multiplier 88hence computes the modification torque ΔTA=0. Responsively, the maximumpump torque TP is not reduced and remains at TPmax, and the matchingpoint is positioned at the point G in FIG. 7. As a result, the deliveryrate of the hydraulic pump 12 is not reduced, and the bucket speed canbe raised to increase the amount of work carried out.

Further, when the bucket strikes against hard earth and sand duringtravel, the traveling speed is slowed down and the torque converterspeed ratio e becomes e=about 0.2 in some cases. On that occasion,because of the traveling state determining unit 85 setting therein therelationship between e and α such that α is reduced at a predeterminedgain as the torque converter speed ratio e increases, a value of 0<α<1depending on the speed ratio e is computed as the determinationcoefficient α. In this case, therefore, since the relationship of β>α isheld, the selector 87 selects the determination coefficient α andoutputs γ=α as the determination coefficient γ. Responsively, themultiplier 88 computes the modification torque ΔTC (negative value) as avalue increased depending on α (i.e., ΔTC having a decreased absolutevalue). Thus, the maximum pump torque TP is reduced from TPmax and theengine torque TEP available for travel is given as a value between thesolid line and the broken line in FIG. 6. As a result, in comparisonwith the case of the maximum pump torque TP being at TPmax, the travelforce is increased and the workability is improved. Stated another way,since the amount by which the maximum pump torque TP is reduced isadjusted depending on a magnitude of the travel torque (speed ratio e)demanded by the traveling system 3, it is possible to perform themaximum pump torque reducing control in a finer manner and to furtherimprove the workability. In addition, the travel torque or the pumpdelivery rate can be prevented from changing abruptly.

With this embodiment described above, the maximum pump torque reducingcontrol can be performed while accurately confirming a work situationduring the combined operation of the travel and the working actuator.Hence, satisfactory combination in work can be maintained and animprovement of both the workability and the working efficiency can berealized.

A second embodiment of the present invention will be described withreference to FIGS. 10 and 11. Note that, in FIGS. 10 and 11, componentsidentical to those in FIGS. 1 and 4 are denoted by the same symbols.

In FIG. 10, a traveling hydraulic working machine according to thisembodiment comprises an engine 1, a working system 2, a traveling system3, and a control system 4A. The working system 2 and the travelingsystem 3 have the same constructions as those in the first embodimentshown in FIG. 1.

The control system 4A includes, in addition to the components in thefirst embodiment shown in FIG. 1, a pressure sensor 61 for detecting, asthe operating situation of the working system 2, the pilot pressure inthe direction in which the hydraulic actuator 13 is contracted (i.e.,the boom-lowering pilot pressure) from among the pilot pressuresoutputted from the control lever units 23. A controller 48A executespredetermined arithmetic and logical operations based on signals fromthe position sensor 43, the pressure sensor 44, the revolution sensors45, 46 and the pressure sensor 61, and then outputs a command signal tothe torque control solenoid valve 29.

In FIG. 11, the controller 48A has, in addition to the functions shownin FIG. 4, the functions of a second working state determining unit 91and a multiplier 92.

The second working state determining unit 91 receives a detected signalof the boom-lowering pilot pressure from the pressure sensor 61, andrefers to a table, which is stored in a memory, based on the receivedinput, thereby computing a third determination coefficient εcorresponding to the boom-lowering pilot pressure at that time. Thethird determination coefficient ε is set with intent not to increase thetravel force without modifying the maximum pump torque when an operationof lowering the boom is performed (i.e., with the intent to increase thetravel force by modifying the maximum pump torque only when theexcavation work is performed while the boom is raised). In the tablestored in the memory, the relationship between the boom-lowering pilotpressure and the third determination coefficient ε is set such that ε=1is set when the boom-lowering pilot pressure is small, and ε=0 is setwhen the boom-lowering pilot pressure rises to some extent.

The multiplier 92 multiplies the modification torque ΔT computed by themodification torque computing unit 83 by the third determinationcoefficient ε, thereby providing a modification torque ΔTB. Theabove-mentioned multiplier 88 multiplies the modification torque ΔTB bythe determination coefficient γ, thereby providing a modification torqueΔTA.

With this embodiment thus constructed, during the work carried out withthe boom lowering operation, the third determination coefficient ε=0 iscomputed and the modification torque ΔTB=0 is resulted. Therefore, themaximum pump torque reducing control is not performed and the travelforce is avoided from increasing during the work.

If the front load is increased and the maximum pump torque reducingcontrol is performed in a state where, for example, snow removing workis carried out at a constant speed while lowering the boom, the travelforce is increased and the snow removing work cannot be carried out atthe constant speed.

In this embodiment, the boom-lowering pilot pressure is detected todetermine whether the work carried out at that time is the excavationwork or the other type of work. When the boom-lowering pilot pressure isdetected, the multiplier 92 computes the modification torque ΔTB as 0and makes the maximum pump torque reducing control disabled. As aresult, even if the front load is increased in the state where, forexample, the snow removing work is carried out at a constant speed whilelowering the boom, the travel force is not increased and the snowremoving work can be carried out at the constant speed.

With this embodiment, therefore, the maximum pump torque reducingcontrol can be performed while accurately confirming a work situationduring the combined operation of the travel and the working actuator.Hence, satisfactory combination in work can be maintained and animprovement of both the workability and the working efficiency can berealized.

Although the foregoing embodiments have been described in connectionwith the case where the traveling hydraulic working machine is atelescopic handler, similar advantages to those described above can alsobe obtained with application of the present invention to other types oftraveling hydraulic working machines so long as they are equipped withtorque converters. Examples of the traveling hydraulic working machineequipped with torque converters, other than the telescopic handler,include a wheel shovel and a wheel loader.

1. A traveling hydraulic working machine comprising at least one primemover (1), a machine body (101) mounting said prime mover thereon,traveling means (3) provided in said machine body and including a torqueconverter (31) coupled to said prime mover, a variable displacementhydraulic pump (12) driven by said prime mover, at least one workingactuator (13-16) operated by a hydraulic fluid from said hydraulic pump,and an operating device (23-26) for generating an operation signal tocontrol said working actuator, wherein said traveling hydraulic workingmachine further comprises: first detecting means (45, 80, 82, 83) fordetecting whether the sum of absorption torque of said hydraulic pump(12) and travel torque of said traveling means (3) exceeds output torqueof said prime mover (1); second detecting means (45, 46, 84, 85) fordetecting an operating situation of said traveling means (3); and pumptorque modifying means (83, 88, 89) for modifying maximum absorptiontorque of said hydraulic pump depending on the operating situation ofsaid traveling means detected by said second detecting means when saidfirst detecting means detects that the sum of the absorption torque ofsaid hydraulic pump and the travel torque exceeds the output torque ofsaid prime mover.
 2. The traveling hydraulic working machine accordingto claim 1, wherein said pump torque modifying means comprises firstmeans (83) for computing a modification torque when said first detectingmeans (45, 80, 82, 83) detects that the sum of the absorption torque ofsaid hydraulic pump (12) and the travel torque exceeds the output torqueof said prime mover (1), second means (88) for modifying themodification torque depending on the operating situation of saidtraveling means (3) detected by said second detecting means (45, 46, 84,85), and third means (89) for controlling the maximum absorption torqueof said hydraulic pump to be reduced by an amount corresponding to themodification torque modified by said second means.
 3. The travelinghydraulic working machine according to claim 2, wherein said seconddetecting means is means (45, 46, 84, 85) for detecting, as theoperating situation of said traveling means (3), an operating situationin which said traveling means requires what magnitude of travel torque,and said second means (88) modifies the modification torque to bereduced or to become 0 when said second detecting means detects thatsaid traveling means is in an operating situation not requiring arelatively large travel torque.
 4. The traveling hydraulic workingmachine according to claim 2, wherein said second means (88) modifiesthe modification torque to be variably reduced to 0 depending on themagnitude of travel torque required by said traveling means (3).
 5. Thetraveling hydraulic working machine according to claim 1, furthercomprising third detecting means (44, 86) for detecting an operatingsituation of said working actuator (13-16), wherein said pump torquemodifying means (83, 88, 89) modifies the maximum absorption torque ofsaid hydraulic pump depending on the operating situation of saidtraveling means detected by said second detecting means (45, 46, 84, 85)and the operating situation of said working actuator detected by saidthird detecting means when said first detecting means (45, 80, 82, 83)detects that the sum of the absorption torque of said hydraulic pump(12) and the travel torque exceeds the output torque of said prime mover(1).
 6. The traveling hydraulic working machine according to claim 5,wherein said pump torque modifying means comprises first means (83) forcomputing a modification torque when said first detecting means (45, 80,82, 83) detects that the sum of the absorption torque of said hydraulicpump (12) and the travel torque exceeds the output torque of said primemover (1), second means (87, 88) for modifying the modification torquedepending on the operating situation of said traveling means detected bysaid second detecting means (45, 46, 84, 85) and the operating situationof said working actuator (13-16) detected by said third detecting means(44, 86), and third means (89) for controlling the maximum absorptiontorque of said hydraulic pump to be reduced by an amount correspondingto the modification torque modified by said second means.
 7. Thetraveling hydraulic working machine according to claim 6, wherein saidthird detecting means is means (44, 86) for detecting, as the operatingsituation of said working actuator (13-16), an operating situation inwhich said working actuator requires what magnitude of pump deliveryrate, and said second means (87, 88) modifies the modification torque tobe reduced or to become 0 when said third detecting means detects thatsaid working actuator is in an operating situation requiring arelatively large pump delivery rate.
 8. The traveling hydraulic workingmachine according to claim 6, wherein said second means (87, 88)modifies the modification torque to be variably reduced to 0 dependingon the magnitude of pump delivery rate required by said working actuator(13-16).
 9. The traveling hydraulic working machine according to claim1, wherein said first detecting means is means (45, 80, 82, 83) fordetecting whether a deviation between a target revolution speed and anactual revolution speed of said prime mover (1) exceeds a preset value,and whether the sum of the absorption torque of said hydraulic pump (12)and the travel torque of said traveling means (3) exceeds the outputtorque of said prime mover is detected depending on whether thedeviation between the target revolution speed and the actual revolutionspeed of said prime mover exceeds the preset value.
 10. The travelinghydraulic working machine according to claim 1, wherein said seconddetecting means includes means (45, 46) for detecting input and outputrevolution speeds of said torque converter (31), and means (84) forcomputing a torque converter speed ratio from the input and outputrevolution speeds of said torque converter, and said second detectingmeans detects the operating situation of said traveling means (3) basedon the torque converter speed ratio.
 11. The traveling hydraulic workingmachine according to claim 5, wherein said third detecting meansincludes means (44) for detecting one of a delivery pressure of saidhydraulic pump (12) and a driving pressure of said working actuator(13-16), and said third detecting means detects the operating situationof said working actuator based on the detected pressure.
 12. Thetraveling hydraulic working machine according to claim 5, wherein saidthird detecting means includes means (61) for detecting the operationsignal generated by said operating device and detects the operatingsituation of said working actuator (13-16) based on the detectedoperation signal.